System for localizing trains along a track



1963 JEAN-CLAUDE SIMON ETAL 3,403,646

SYSTEM FOR LOCALIZING TRAINS ALONG A TRACK 4 Sheets-Sheet 1 Filed May 9,1967 1 u awn u 55 it w. A h

1968 JEAN-CLAUDE SIMON ETAL 3,408,645

SYSTEM FOR LOCALIZING TRAINS ALONG A TRACK 4 Sheets-Sheet 5 Filed May 9,1967 JEANCLAUDE SIMON ETAL 3,408,646

SYSTEM FOR LOCALIZING TRAINS ALONG A TRACK Oct. 29, 1968 Filed May 9,1967 4 Sheets-Sheet 4 Fig.6

Fig.9

RECEIVER DIRECTIONAL COUPLER 4 TRANSMITTER Fig.10

United States 3,408,646 SYSTEM FOR LOCALIZIN G TRAINS ALONG A TRACKJean-Claude Simon and Georges Jean Broussaud, Paris, France, assignorsto CSF-Compagnie Generale de Telegraphie Sans Fil, a corporation ofFrance Filed May 9, 1967, Ser. No. 637,187 Claims priority,applicltionoFrance, May 16, 1966,

,so 10 Claims. (31. 343-65) ABSTRACT OF THE DISCLOSURE The presentinvention relates to safety systems for controlling the train traflicalong a track.

The conventional solution of this problem consists in defining tracksections and providing signalling devices for preventing collisions, forexample by preventing that two trains may -be simultaneously in the samesection. This solution is no longer appropriate, in view of the risingtraflic density, which necessitates an increase in the speed, thefrequency and the length of trains which are permitted to run along thesame track. It is also subject to atmospherics which can affect theinterpretation of signals optically transmitted to the driver.

A modern solution of problems of detection and telemetering is providedby radar systems. However, most of radar systems are based on theangular detection of targets by means of a highly directional antennaradiating into space. This is obviously superfluous for locating trainsrunning along a track and it is suitable to use the track itself forguiding the radioelectric control signals. Unfortunately, railway railshave a geometry which lends itself badly for guiding electromagneticwaves. This results in the use of complex transmission lines for guidingthe waves parallel to the track.

According to the present invention there is provided a system forlocating trains of cars along a track comprising a dielectric waveguide, extending along said track, for receiving ultra-high frequencywave energy from said cars and propagating said energy as a surface waveand reflector means spaced along said track for reflecting said energytowards said cars.

For'a better understanding of the invention and to show how the same maybe carried into effect, reference will be made to the drawingsaccompanying the following description and in which:

FIG. 1 is a view in perspective of a carriage moving along a track;

FIG. 2 is a plan view showing the principle of the system according tothe invention;

FIG. 3 is an elevation view of the track equipped with responders;

FIG. 4 is a block diagram of the radioelectric locating system;

FIG. 5 is an explanatory drawing;

FIG. '6 shows in elevation a first device for exciting ultra-highfrequency Waves;

FIG. 7 is an end view of a second device for exciting ultra-highfrequency waves;

atent FIG. 8 is a transverse section of one embodiment of a responder;

FIG. 9 is an end view of a third embodiment of a device for excitingultra-high frequency waves; and

FIG. 10 is a plan view of the arrangement of FIG. 9.

FIG. 1 shows a track 1 of a special type along which moves a carriage 2,only the outline of which has been drawn. By way of non-limitativeexample, the track 1 has the form of a horizontal T shaped concrete beamhaving a base EFGH. The carriage 2 floats on this track, being supportedthere upon on a cushion of air. However, without departing from theprinciple of the invention, the construction may be modified to compriserails and wheels adapted to roll the carriage 2 along the track 1.

According to the invention, a part of the track 1 behaves after themanner of a dielectric waveguide with the axis 0z, having in the planexoy a predetermined transverse cross-section ABCD. In FIG. 1, thiscrosssection is formed by the vertical arm of the concrete beam 1. Onboard of the carriage 2, excitation means 3 are provided, which arecoupled to the track 1, serving as a waveguide, in order to excitetherein a surface wave, progressing parallel to o z. FIG. 2 shows thefront of a train 21 and the rear of a train 22, which precedes theformer one. The train 21 is equipped with an ultra-high frequency system4, adapted to transmit and to receive locating signals via antennae 3,connected to the vertical arm of the runway ,1. Inside the environmentwith the refraction index 1 and the permittivity e forming thedielectric guide, the transmitted waves suffer a total reflection, whentheir incidence 0 is greater than the critical angle 0,, given by sin 0m where 1 is the index of the environment surrounding the guide.

Under these conditions, a surface wave can be formed about thedielectric guide and may progress along o z with a phase velocity vgiven by the formula:

cos 0 where is the phase velocity of electromagnetic waves in theenvironment with the index 1 It can be shown that the surface waveexcited around the guide with the width a is damped exponentially withincreasing distance from the lateral surfaces of the guide. It can alsobe shown that the efiicient section, where the electromagnetic field hasan attenuation less than He, has a radius p with int. 1 oxt. P 2

It is therefore possible to use the dielectric guide for propagatingwith low attenuation a surface wave which remains confined within theimmediate vicinity of the track 1. If the surface wave encounters duringits progression along the track a conducting obstacle, such as the rearof the train 22, the electromagnetic energy is reflected in the samewave mode towards the train 21 which receives a delayed echo in responseto the incident wave train. The guiding of the wave is still effectiveif the guide is slightly curved. Amongst the modes capable of beingpropagated in the form of surface waves about a dielectric waveguide,may be mentioned the mode TM shown in FIGS. 1 and 2; it is also possibleto excite a TE mode or a hybrid TEM mode.

According to a first embodiment of the radioelectric system according tothe invention, one branch of the track 1 is used as dielectric guide.The permittivity of the concrete used being three times as high as thatof air, and the losses remaining small at the intended frequencies, itcan be shown that, with a carrier frequency of 300 to 500 mc./s., a beamone metre high and 40 cm. thick can transmit a surface wave having alinear attenuation of a.

few decibels per kilometre.

Taking into account possible homogeneity defects, ranges of severalkilometres are possible with a transmitting power of a mean value of afew watts.

FIG. 3 shows, in elevation, a track 1 and two trains 21 and 22 movingone behind the other from the left to the right. At regular intervals P(for example, of one kilo metre), responder beacons 5 have beenincorporated into the track, which, on interrogation by the locatingsystem mounted on board the train 21, transmit according to apredetermined code a surface wave directed towards this system.

According to the invention, the beacons p, p+1, p+2, p+i p-l-k, areinterrogated one after the other by the radioelectric system mounted onboard the train 21, and if no train 22 is between it and the train 21,the beacons 5 supply k-l-l coded information items, which enable theradioelectric system of locating instantaneously the exact position ofthe train 21. In the case that the train 22 masks the (p+i)th beacon 5,the surface wave coming from the train 21 is reflected by the train 22without interrogating the following beacons; the telemetering system ofthe train 21 receives 1 coherent information items instead of k+1 and itmay be concluded that there is an obstacle or that there is a failure inthe operation of the beacons, which necessitates anyway the stopping ofthe train 21.

In FIG. 4, an embodiment is shown of a block diagram of theradioelectric system according to the invention. The dielectric guide 1is connected to an antenna 3, comprising for example an array ofradiating elements and phase shifting means, for excitating a surfacewave propagating towards the right and for picking up the wavepropagating in the opposite direction. With the dipoles shown in FIG. 4,a surface wave TM can be excited the electrical and magnetic vectors ofwhich are shown in FIG. 1. The antenna 3 is coupled through adirectional coupler 6 to an ultra-high frequency transmitter 7 and to anultra-high frequency receiver 8; the transmitter 7 is modulated by amodulator 10 which causes a frequency modulation in the shape ofsymmetrical saw-teeth. The output of the receiver 8 feeds bandpassfilters 11, 12, 13, 14 and 15 which separate, in accordance with theirrespective frequencies, the different locating signals collected by theantenna 3. The locating signals transmitted by the filters 11, 12 and 13are compared in a telemetering system 16 according to the law ofmodulation provided by the modulator 10, in order to determine theirrespective propagation times. These times are then compared betweenthemselves by means of a correlator 17 which supplies the indication ofthe position z,, of the vehicle carrying the radioelectric system. Adifferentiator 18, connected to the output of the correlator 17 givesthe absolute velocity v of the train. The filter 14 transmits directlyto a detector 19 a fixed echo 7 produced by means of a resonant cavity9, a socalled echo-box, permanently connected to the output of thetransmitter 7. This makes it possible to control permanently theoperation of the transmit-receive assembly. The filtre 15 transmits anecho caused by the reflection from an obstacle 22, located at anydistance z in front of the transmitting vehicle 21; this echo is mixedwith a signal transmitted by the antenna 3 in a mixer 23, which suppliesa signal whose frequency is proportional to this distance. A frequencydiscriminator 24 converts this measuring signal into the distance Zwhich is applied to a differentiator 25 to supply the relative speed vof the transmitting vehicle 21 relative to the obstacle 22. Theinformation z 2,, v v and 'y are finally applied to a circuit 26 whichensures the control of the propulsion unit of the train 21.

FIG. 5 shows at (a) the variation as a function of the time of thefrequency of the signal transmitted by the radioelectric system of FIG.4. The transmission wave is continuous and propagates as a surface Wavealong the dielectric guide 1. During its propagation in front of thevehicle 21, the wave encounters the beacons 5 which are frequency codedso as to reflect a signal only if its frequency has a certain value. Thebeacon p responds to the frequency of interrogation f the beacon p+1responds to the frequency fp-I-l and so on, and the echoes received areEp, Ep+1, Ep+2 etc., in accordance with the diagrams (b), (c) and (d) inFIG. 5. It may be seen, upon comparing these diagrams with the diagram(a), that the propagation times r, r-l-R, r+2R are directly related tothe distances p, p+-P, and p+2P which separate the beacons 5 from thetrain 21 in FIG. 3. Hence, from these times, the absolute position ofthe train 21 along the track 1 can be calculated. If the propagationtime r+2R is abnormally small, it may be assumed that an obstacle 22masks the beacon p+2 which should have determined its duration. Thisabnormality reveals primarily the presence of an obstacle between twoconsecutive beacons. This obstacle is also detected by an intensive echowhich it returns towards the receiver of the radioelectric system. Thisecho, delayed as a function of the propagation distance, has a frequencymodulation delayed relative to that of the transmitted wave. Diagram (e)shows in solid lines the modulation of the received echo and in brokenlines that of the transmitted wave and it may be readily seen that thegap A is proportional to the distance 2,- separating the train 21 fromthe obstacle 22. By measuring the frequency gap A a second means isprovided for locating the obstacle along the track 1. These two methodsof location insure a great operational reliability of the system andprovide valuable information for controlling the run of the vehicles.The echo-box 9 affords additional safety since it creates a systematicecho 7, such as is shown in the diagram (f) in FIG. 5 which makes itpossible to control permanently the operation of the transmit-receiveassembly.

Without thereby departing from the principle of the invention, the blockdiagram shown in FIG. 4 may be modified in many ways. More particularly,the radioelectric system may be pulse modulated. This makes it possibleto use in the receiver a compression method which improves the precisionin the locating of targets. In this case, the beacons may be coded, forretransmitting a pulse train forming a digital position code. Whateverthe method adopted, it is possible, without using pulse compression, todetermine distances within :15 metres with a radioelectric systemtransmitting within a frequency band of 50 mc./s. This band may bereduced by providing the suitable information processing and thisreduction is limited only by the signal-to-noise ratio which is anywayfavourable in view of the small ranges required.

If the modulation shown diagrammatically in FIG. 5 is used, it can bereadily shown that the choice of symmetrical saw-teeth makes it possibleto compensate frequency shifts caused by the Doppler-Fizeau effect. Itis also possible to utilise systematically this measurable effect as ameans for determining the speeds at which the train is approaching thebeacons and fixed or mobile obstacles.

FIG. 6 shows in elevation a track 1 and an antenna of the YAGI type,capable of exciting about the vertical arm of the track 1 a surface waveaccording to the TE mode. The aperture of the antenna 31 must cover theeiiicient section of the surface wave which leads to arrange the antennaon either side of the vertical arm of the track 1.

FIG. 7 shows an end view of an antenna with distributed excitation. Itcomprises an electrode 32 sliding over the top of the track 1 and a pairof electrodes 33, connected electrically. The electrodes 32 and 33 forman excitation line with the axis parallel to the track 1. This line iscoupled to a radiating line formed by two dielectric plates 34 whichexcite the surface wave according to one of the modes TE, TM or TEM.

FIG. 8 shows diagrammatically a responder beacon 5 embedded in thetrack 1. It consists of a radiating element 51 placed into a cavityformed in the wall of the track 1. This element is weakly coupled withthe surface wave whose efiicient cross-section surrounds the verticalarm, acting as a dielectric guide. The element 51 is electricallycoupled through a directional coupler 52 with a receiver 53 and atransmitter 54 which are both tuned to a predetermined frequency f,,,depending on the rank of the beacon. When the beacon is interrogated bya signal with the frequency f the receiver 53 controls theretransmission of the same frequency f by the transmitter 54.

FIG. 9 shows an end view of a track 1 surmounted by a dielectric guide100. This arrangement is used where the vertical arm of the beam 1 isunsuitable for guiding the surface wave. This is the case wherecentimetre waves are used in preference to metre waves. For exciting thesurface wave around the guide 100, an antenna according to FIG. 10 isused. It comprises an exciter waveguide 104, one end of which isequipped with a dielectric block 103, cut to a wedge in order to obtaina gradual coupling with the efficient section of the wave to be excitedaround the guide 100. The guide 100 can be formed from a dielectric withlow losses at the frequencies used. It may also be formed of a periodicarray of conducting obstacles forming an artificial dielectric.

Of course the invention is not limited to the embodiments described andshown which were given solely by way of example.

What is claimed is:-

1. A system for locating trains of cars along a track comprising adielectric wave guide extending along said track for receiving ultrahighfrequency wave energy from said cars and propagating said energy as asurface wave and a plurality of passive responder-beacons spaced longsaid track and programmed for reflecting received energy towards saidcars in accordance with a predetermined code.

2. A system as claimed in claim 1, wherein said wave guide is a concretebeam.

3. A system as claimed in claim 1, wherein, said train being shaped forfloating along the vertical branch of a T shaped beam, resting upon itshorizontal branch, said wave guide is said vertical branch.

4. A system as claimed in claim 1, wherein said guide is an artificialdielectric guide.

5. A system as claimed in claim 1, wherein said responder-beacons areprogrammed for responding to respective predetermined frequencies only.

6. A transmit-receive system for transmitting from cars ultrahighfrequency energy and for receiving echoes from responder-beacons andobstables in a system as claimed in claim 1 comprising transmitter meansfor exciting a surface wave along said wave guide in the direction ofmotion of said cars, receiving means for picking up said surface wave asreflected by said responder-becaons and obstacles ahead of said cars,first metering means, coupled to said receiving means, for measuring thedistance from said obstacles to said cars and second metering means,coupled to said receiving means, for determining, from said echoes fromsaid responder-beacons, the position of said cars along said track.

7. A system as claimed in claim 6, further comprising means fordifferentiating said position and said distance with respect to time forrespectively determining the absolute speed of said cars and therelative speed of said cars with respect to said obstacles.

8. A system as claimed in claim 6, wherein said excitation meanscomprises an end-fire antenna.

9. A system as claimed in claim 8, wherein said antenna comprises twoelements respectively coupled to the two sides of said wave guide.

10. A system as claimed in claim 6, wherein said transmitter meanscomprise means for frequency modulating said surface wave and saidsecond metering means comprises a plurality of channels respectivelytuned to different frequencies respectively corresponding to differentresponder-beacons.

References Cited UNITED STATES PATENTS 3,305,682 2/1967 Bolster et al.246167 2,716,186 8/1955 Ford 246-l87 2,702,342 2/1955 Korman 2461872,698,377 12/1954 Korman 7A6-187 FOREIGN PATENTS 1,378,440 10/ 1964France.

939,248 11/1948 France.

RODNEY D. BENNETT, Primary Examiner.

C. L. WHITHAM, Assistant Examiner.

